Between 2013-2017, Apple shipped laptops equipped with proprietary but very fast SSD.
Those SSDs were PCIe-based AHCI "blade" SSDs with a proprietary "gumstick connector" (12+16 pins), either made by Toshiba or Samsung (SSUAX or SSUBX).
For many years the only possible replacements or upgrades for those SSD were to a) replace with SSDs pulled from other Apple laptops, or b) buy expensive third-party SSDs from vendors like OWC or Transcend, or c) take your chances with DIY solutions like buying a M.2 AHCI SSD with an adapter e.g. Samsung 941 or Samsung 950 SSDs.
These PCIe AHCI SSD are no longer made, so you can't buy new ones, and used ones are expensive with low capacity and no warranty.
At the same time, NVMe "blades" M.2 SSD are going more on more mainstream on the PC market, and there are literally dozens of brand new, cheap, super fast and reliable NVMe SSD on the market, with enormous capacities up to 2TB (and maybe more in the future).
So why not go NVMe ?
To gain full NVMe support you need two things :
- support at the BootRom (firmware) level
- support at the OS level
Hopefully, in 2017, macOS
10.13 (High Sierra) came out and it was discovered that it not only supported
any tiers NVMe SSD but it also brought BootRom upgrades which enabled booting with NVMe SSD...
Yay!
So, now we can upgrade many 2013-2017 MacBook laptops with brand new, cheap NVMe SSDs carrying 3 to 5-years warranty, instead of expensive, used, out of warranty, AHCI SSDs.